From midnight anyone buying a property for £500,000 or more through a company structure now has to pay a 15% stamp duty charge as the chancellor cracked down on wealthy "buy-to-leave" investors.

The government said it would reduce the threshold for the tax charge from the £2m it set in 2012 to homes worth £500,000 – a move that is likely to catch many of those buying an investment property in central London.

The Treasury will also reduce the threshold for its annual tax on dwellings bought through a company "envelope" to £500,000, although that will be a staggered change, beginning in April 2015 with the introduction of a £7,000 a year charge on homes worth between £1m and £2m. The tax on homes worth above £2m has raised five times the amount of tax forecast for 2013/14, and the government said it believed it could discourage the use of corporate envelopes to invest in high value UK housing which is then left empty or underused.

However, estate agents in some of London's wealthiest boroughs said the tax changes were unlikely to deter investors. Sue Foxley, research director at Cluttons, said: "It is debatable whether this will have an impact on appetite from international buyers as despite this new transactional cost, London property is still an attractive investment with potential significant capital growth."

The role of overseas investors in stoking London house prices has been a hot topic in recent months, and Miles Shipside from the property website Rightmove said some people trying to buy average-priced homes in the capital had been at a disadvantage to investors using corporate structures to escape tax. He added: "Londoners now have a minimum 10% bidding advantage courtesy of lower stamp duty before they end paying an overall cost equivalent to a company structure buyer."